The invention is directed to improvements in vehicle brake systems.
German Offenlegungsschrift No. 36 12 793 discloses a vehicle brake system having a hydraulic brake booster, an auxiliary cylinder and an auxiliary piston and having a valve assembly as an anti-skid device, and with a pressure source for supplying the brake booster. Triggering the valve assembly actuates the auxiliary piston, which thus counteracts a booster piston of the brake booster, thereby reducing the brake pressures in a master brake cylinder of the brake system and overcoming the danger of skidding. Other valve assemblies are disposed between this master brake cylinder and the wheel brakes so that in the wheel brakes at which there is no danger of skidding, the brake pressures can be kept constant.
United States Patent to Bertling et al. U.S. Pat. No. 4,416,347 discloses a vehicle brake system having a hydraulic brake booster and a device that functions as an anti-skid device or as a drive slip limitation device, as needed. In both modes, the actuation of the at least one brake booster piston is controlled by means of a valve assembly, for both brake pressure generation and brake pressure modulation. In the anti-skid situation, the pressure from a brake valve that supplies the brake booster is modulated by the valve assembly. In the situation where drive slip is being limited, pressure fluid is sent from a pressure source directly into the brake booster by means of the valve assembly. The disadvantage is that whenever anti-slip operation must be interrupted in favor of anti-skid operation, at least one of the master brake cylinder pistons is not in its normal outset position.